A fixed communication network generally allows data or voice to be communicated between fixed terminals. An example of such a network is a public switched telephone network (PSTN) in which subscribers communicate using fixed telephone sets. Other examples include wired local-area networks (LANs) and wide-area networks (WANs), which are mainly used for transmission of data between computers. Fixed communication networks tend to restrict mobility of the users. If the user moves, they often have little choice but to disconnect their terminal from the network and reconnect at a different location. This is inconvenient for the user since network connection is temporarily lost. Moreover, network reconnection is not without its problems, particularly as it requires a connection point at the new location.
A mobile communication network helps to overcome these problems. An example of such a network is a public land mobile network (PLMN) such as the global system for mobile communication (GSM) network. Mobile terminals exchange signals with geographically-spaced base stations included in the network using radio signals. This allows the user to make and receive calls within a large area, even while moving. Mobility is achieved not only because wireless connections are used, but also because the mobile terminal is dynamically allocated a suitable base station. Thus, if the user is moving, a connection to one base station can be dropped and a new connection to another base station can established automatically so as to provide seamless coverage.
Mobile communication networks and mobile terminals are becoming increasingly common. For example, so-called 2nd generation mobile telecommunication systems, such as GSM networks, are being replaced by 3rd generation systems, such as universal mobile telecommunications standard (UMTS) networks. Moreover, users are becoming more reliant on their mobile terminals. Therefore, it is important that users are able to access the mobile communications network freely.
However, access can be restricted by the connections provided by base stations. For example, at a physical level, a radio link between the terminal and the base station may be of poor quality. This can happen when the user is located indoors. Alternatively, at a resource level, the base station may not be able to provide sufficient channels to mobile terminals requiring service. This often occurs when a large number of people gather at one place, for example at a sports stadium.
A solution to this problem is to provide additional base stations. However, this solution is expensive and relies upon being able to find suitable sites for the additional base stations.
Another solution is to employ mobile terminals as relays. For example, “On the Relaying Capability of Next-Generation GSM Cellular Networks” by George Neonakis Aggélou and Rahim Tafazolli, pp. 40-47, IEEE Personal Communications (February 2001) describes a terminal which is able to relay data using an ad-hoc GSM (A-GSM) network.
The present invention seeks to provide an improved mobile communications network for mobile terminals.